In glass applications such as liquid crystal panels, optical communication devices for instance optical filters and optical switches, recording medium, halogen, High Intensity Discharge (HID) lamps, etc. the consistency of the glass substrate properties is quite critical. High-energy laser systems employ multiple large pieces of optical quality glass, sometimes thousands of large size laser glass pieces, and it is imperative for the pieces to have consistent optical quality. Glass compositions, similarly to fused quartz compositions, are characterized by a few fundamental properties affecting the manufacturing of or the properties of products employing the compositions, i.e., viscosity, percent transmission, OH level to name a few. The effect of OH (hydroxyl) on viscosity of glass or quartz is widely known. FIG. 1, for instance, illustrates the viscosity curves of high purity quartz made with various OH concentrations. As seen from the Figure, viscosity of glass drastically drops with increased hydroxyl concentration. If glass or quartz has batch-to-batch or within-batch variations in the OH level, it will result in inconsistent manufacturability and product quality. From a lamp manufacturer's perspective, variations in the glass properties impact the yields of the high-speed lamp production lines, requiring undesirable and frequent adjustments made to the equipment to account for the variations in the glass properties.
Almost all arc discharge lamps and many high intensity filament lamps, such as tungsten-halogen lamps, emit ultraviolet (UV) radiation which may be harmful to human eyes and skin. As disclosed in U.S. Pat. Nos. 2,895,839; 3,148,300; 3,848,152; 4,307,315 and 4,361,779, lamps have been developed having a light source which emits both UV and visible light radiation enclosed within a vitreous envelope of fused quartz. U.S. Pat. Nos. 2,221,709; 5,569,979; 6,677,260 disclose fused quartz compositions containing UV-absorbing materials, or dopants as they are called, in the form of tubings or rods for use in making lamps, e.g., as lamp envelopes with properties to absorb UV radiation.
United States Patent Publication No. 2004/0063564A1 discloses a composition useful for forming glass substrates for use in information recording medium, with desirable properties such as specific linear thermal expansion coefficient, fracture toughness, and a predetermined surface hardness. In applications for making bulk glass articles such as fiberglass, it is also useful to have consistency in the glass compositions to obtain the desired ranges of properties such as viscosities, humidity resistance, and the like. United States Patent Publication No. 2002/0077243A1 discloses a composition for making glass fiber filters for use in micro-electronic clean room environments.
Due to the bulk volume of the feedstock making up the glass composition, there is a wide batch-to-batch variation in glass compositions as well as in the properties of products made from glass compositions of the prior art. It is important to have consistent properties in a glass composition such that products made thereof have properties that are uniform or varying in a narrow range. Additionally, the consistent properties allowing manufacturers to run production lines with minor or no adjustments in the line, for high productivity and consistently good glass products. The invention relates to a novel glass composition and a method for making glass products with uniform properties, as measured by the standard deviation.
In addition to the considerations above, various applications require specialized silica glass that possesses both a decreased brittleness when compared with various forms of typical silica glass, or even high silica glass, and a decreased density when compared to other silica, or high silica, glasses. While not wishing to be bound to any one use, a silica glass with reduced brittleness and reduced density would be useful in a wide range of applications where increased strength and reduced weight per unit volume of glass is desirable.
Given this, there is a need in the art for a silica glass that achieves an increase in strength while simultaneously achieving a reduction in brittleness thereby permitting such a glass to be used in a wide range of applications.